Influence of the Occupying Proportion of Mineralised Particles Within the Grafted Volume on Subsequent Volume Shrinkage: A Preclinical Study on Rabbit Calvaria

AIM: To evaluate whether mineral particle occupancy within the grafted volume influences volumetric stability and bone regeneration, and to compare particulate grafts, collagenated grafts, hyaluronic acid-conjugated particulates and mechanical manipulation in a vertical augmentation model. MATERIALS AND METHODS: Ten New Zealand white rabbits received four standardised vertical calvarial defects and filled with saline-hydrated particulate deproteinised porcine bone mineral (Control), intact collagenated bone blocks (CBM), hydrated and mechanically crushed collagenated blocks (cCBM) or particulate grafts mixed with hyaluronic acid (HA). Grafts were placed in sealed plastic cylinders. Animals were sacrificed at 2 and 8 weeks. Volumetric stability and mineralised tissue volume were assessed by micro-computed tomography, and the total augmented area, new bone formation, residual material and particle length were evaluated by histological and histomorphometric analyses. Data were analysed using linear mixed-effects models. RESULTS: Mineralised tissue volume increased over time in Control, CBM and HA groups but decreased in cCBM (time × material interaction, p = 0.020). At 8 weeks, total augmented area was preserved in Control and CBM, whereas significant volumetric shrinkage occurred in cCBM and HA (p < 0.01). New bone formation increased in all groups but was highest in the Control group. Residual material area remained stable but was higher in Control and CBM than in cCBM and HA, and particle length was reduced in mechanically manipulated groups. CONCLUSIONS: Given the limitations of this model, binder incorporation and mechanical manipulation may affect particle occupancy and volumetric stability. Reducing graft manipulation may enhance space maintenance and facilitate bone regeneration.